Linux: Use After Free
CVE-2025-21671 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions fe3de867f94819ba0f28e035c0b0182150147d95, 571d3f6045cd3a6d9f6aec33b678f3ffe97582ef, 902ef8f16d5ca77edc77c30656be54186c1e99b7 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.22% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to fe3de867f94819ba0f28e035c0b0182150147d95 or 571d3f6045cd3a6d9f6aec33b678f3ffe97582ef or 902ef8f16d5ca77edc77c30656be54186c1e99b7 or 212fe1c0df4a150fb6298db2cfff267ceaba5402, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.127 or 6.6.74 or 6.12.11, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | ac3b5366b9b7c9d97b606532ceab43d2329a22f3 up to, but not including, fe3de867f94819ba0f28e035c0b0182150147d95; 0b5b0b65561b34e6e360de317e4bcd031bfabf42 up to, but not including, 571d3f6045cd3a6d9f6aec33b678f3ffe97582ef; 6fb92e9a52e3feae309a213950f21dfcd1eb0b40 up to, but not including, 902ef8f16d5ca77edc77c30656be54186c1e99b7; 74363ec674cb172d8856de25776c8f3103f05e2f up to, but not including, 212fe1c0df4a150fb6298db2cfff267ceaba5402; 6.1.122 up to, but not including, 6.1.127; 6.6.68 up to, but not including, 6.6.74; 6.12.7 up to, but not including, 6.12.11 | fe3de867f94819ba0f28e035c0b0182150147d95, 571d3f6045cd3a6d9f6aec33b678f3ffe97582ef, 902ef8f16d5ca77edc77c30656be54186c1e99b7, 212fe1c0df4a150fb6298db2cfff267ceaba5402, 6.1.127, 6.6.74 |
| Linux | Linux Kernel | 6.1.122 up to, but not including, 6.1.127; 6.6.68 up to, but not including, 6.6.74; 6.12.7 up to, but not including, 6.12.11 | 6.1.127, 6.6.74, 6.12.11 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: zram: fix potential UAF of zram table If zram_meta_alloc failed early, it frees allocated zram->table without setting it NULL. Which will potentially cause zram_meta_free to access the table if user reset an failed and uninitialized device.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Recent Use After Free vulnerabilities
- 8.8 High severity
- 8.4 High severity
- 8.4 High severity
- 8.4 High severity
- 8.4 High severity
- 8.4 High severity
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